In trench field plate FETs (field effect transistors) portions of a conductive field plate are buried in a trench extending into the drift zone. In the blocking mode the source potential applied to the field plate depletes portions of the drift zone between the buried field plate portions. The lateral depletion mechanism allows for increasing the dopant concentration in the drift zone without loss of voltage blocking capability. The increased dopant concentration in turn results in a reduced on-state resistance RDSon. The extension of an overlap of the buried field plate portions with the drift zone as well as thickness and quality of a field dielectric separating the buried field plate portions from the drift zone set the total voltage blocking capability of the trench field plate FET.
It is desirable to provide semiconductor devices and trench field plate FETs with high voltage blocking capability.